1. Field of the Invention
The present invention relates to a structure for mounting a current detection resistor device suitable for use in current detection circuit and the like in a switching power circuit, and relates in particular to a technique of mounting a low resistance resistor device on a circuit board for detecting a large current containing high frequency components that may cause problems of parasitic inductance.
2. Description of the Related Art
In recent years, with the trend towards the use of CPU chips operating at low voltage and large current in electronic devices such as personal computers, switching power source including DC/DC converter and the like has been used for supplying a power to the circuits. In such a switching power circuit, a current detection resistor device is being used in frequency bands ranging from several tens to several hundreds kilo Herz (kHz). A saw-teeth waveform current flows ranging from several amperes to several tens of amperes to detect the magnitude of current on the basis of a voltage generated at the both ends of the low resistance resistor device. In such a current detection resistor device, it is necessary that the resistance be as low as practical, typically less than several mili-ohms and also it is desirable that the parasitic inductance of the resistor device itself be as low as possible. This is because the resistance value of the resistor device itself is low and the frequency is relatively high, so that even for a small inductance at the level of 1 nH, the combined impedance generated at the both ends of the resistor device becomes high to produce voltage detection error.
The present invention is provided in view of the background information described above, an object of the present invention is to provide a structure for mounting a current detection resistor device that can detect, with high precision, a large electrical current that flows in the resistor device in a current detection circuit for a switching power source circuit operating at high frequencies.
Another object of the present invention is to provide a method for measuring an effective inductance value in real-time while the current detection resistor device is in use.
The feature of the mounting structure is that voltage detection terminal wiring is configured so as to extend along current path of the resistor body first, and then, to bend at right angles to the current path, while maintaining electrical isolation from a resistor body of the resistor device.
According to the present invention described above, the wiring pattern is arranged on the circuit board to extend for some distance in the same direction as the current to be measured, thereby causing mutual-inductance between that section of the wiring pattern and the resistor body. This causes cancellation of induced voltage caused by the self-inductance of the resistor body, so that, from the viewpoint of the measuring system, it is possible to nullify detection error generated by the voltage induced by the self-inductance of the resistor body. Therefore, precision determination of current flow is enabled in such cases as a flow of current to be measured in a switching power circuit that contains high frequency components.
Also, the present method of measuring an effective inductance value comprises: connecting to a pair of lands for respective electrodes provided at both ends of a resistor device so as to flow saw-teeth waveform current to be measured through the resistor device; disposing a voltage detection terminal wiring from the lands for detecting a voltage produced between both ends of the resistor device; detecting a flow of current to be measured and detecting a voltage produced by the flow of the current in the resistor device by the voltage detection terminal wiring; and computing the effective inductance value basing on a variation in the flow of current and a corresponding variation in the voltage. Here, it is preferable for the voltage detection terminal wiring to extend inwardly along the central axes of both lands first, and to bend at right angles in opposite directions, along the central axis between the lands, so that one wiring pattern loops to the back side of the substrate through the via-hole on the circuit board to extend towards the direction of other wiring pattern, so that the one wiring pattern and other wiring pattern are aligned and extended in parallel on the front and back surfaces of the circuit board, respectively.
According to the present invention described above, it enables to measure an effective inductance value of the resistor device in-real time in a condition by simulating the actual use of the resistor device. Therefore, it becomes possible to accurately evaluate an effective inductance that greatly affects the measurement errors in resistor devices of lower than several mxcexa9, thereby enabling to predict error voltage generation when the resistor device is used in a switching power source such as a DC/DC converter. Also, because the effective inductance can be measured for low resistance resistor devices in actual conditions of usage, and therefore, it can contribute to manufacturing a low-inductance current detection resistor device that produces virtually no error voltages.
Also, a feature of the current detection resistor device of the present invention is that the lead wires are connected to the electrodes respectively and extended along the current path in the resistor body on a surface of the resistor body, while maintaining electrical isolation from the resistor body; and voltage detection terminals are positioned at the ends of the lead wires.
According to the present invention described above, by extending the lead wires in the same direction as the direction of flow of the current to be measured and providing sufficient length to the lead wires, mutually induced voltage is generated on the lead wires by the current flowing in the resistor body. Accordingly, it enables to nullify induced voltage caused by self-inductance of the resistor body, thereby effectively reducing the error generated by induced voltage by self-inductance of the resistor body, thus accurate voltage (V=Rxc3x97I) is detected at the voltage detection terminals. Therefore, precision determination of current flow is enabled in such cases as a flow of current to be measured in a switching power circuit that contains many high frequency components.
The above and other objects, features, and advantages of the present invention will be apparent from the following description when taken in conjunction with the accompanying drawings which illustrates preferred embodiments of the present invention by way of example.